robichaux



MarCh 3, 1964 T. J. RoBlcHAux METHOD OF TREATING EARTH FORMATIONS Filed Aug. 23, 1962 EARTH FORMATION BE/TREATED INVENTOR THOMAS J, ROBICHAUX BY Jg. 5M

HIS ATTORNEY United States Patent O This invention relates to the treatment of earth formations surrounding oil wells. More particularly, this invention is directed to an improved method for injecting sand-consolidation fluids into subsurface formations in order to consolidate the sands therein and for injecting similar treating fluids into earth formations for other purposes.

ln producing fluids from loosely consolidated subsurface formations, small size particles of unconsolidated formations, such as sand, are produced along with the formation fluids. Because production of sand with its attendant accumulation in the well bore or movement to the surface is undesired, various sand-control measures have been used to inhibit or prevent sand particles from moving into the well bore. One control measure is the use of plastics which bind the sand particles together while permitting flow of well fluids therethrough.

A particularly' outstanding method of consolidating unconsolidated formations utilizes as the treating fluid a single homogeneous solution of polyepoxides with certain amine curing agents capable of imparting surfactant properties to the resulting resin; the various ingredients are selected such that a partially cured reaction product of epoxy resin and amine curing agent separates from the solution after the solution is in place in the formation to be treated and coats the grains of the formation. T he cured product is a thermoset, cross-linked, oil-insoluble resin which produces a consolidated formation of high compressive strength and good permeability. Details of this improved method of consolidating unconsolidated formations are disclosed in copending patent application Serial No. 299,675 of Haavenar and Meys, filed July 13, 1962, corresponding to British application Serial No. 2833/ 62.

When an earth formation is treated with a single solution comprising polyepoxide and curing agent therefor, it is important that the active ingredients be completely displaced from the well bore. It is similarly important that these ingredients be retained in place in portions of the unconsolidated formation immediately adjacent the well bore in order to prevent a condition in which a substantial portion of the formation nearest the well bore remains unconsolidated.

lt is an object of this invention to provide an improved method for displacing treating solutions of polyepoxides and curing agents therefor into underground formations surrounding a borehole, It is a specific object to provide a method which permits displacing a sand-consolidating solution of polyepoxide and curing agent into an unconsolidated formation in such a manner that substantially all of the solution is displaced from the well bore and that no substantial portion of the formation immediately surrounding the well bore remains untreated.

rThese and other objects of this invention will be understood from tue following description, taken with reference to the attached drawing wherein the sole gure is a diagrammatic illustration of a section through a bore-v hole and surrounding formation in which the invention is being practiced.

The improvement of this invention resides in displacing a solution containing sand-consolidating ingredients down through a well bore into a formation surrounding the well bore by a method which comprises pumping said solution into the well bore, thereafter pumping into the well bore a plug of a gelled fluid, and thereafter pumping into the well bore any desired displacing uid, such as water, mud or oil. The consolidating solution comprises a hydrocarbon solvent, a polyepoxide, and in the preferred mode a stoichiometric excess of an amine curing agent therefor which is capable of imparting surfactant properties to the resin. It is particularly preferred to use as the gelled fluid one which reverts to liquid form after a suitable interval at the bottom of the borehole. This facilitates removal of the gelled plug when the well is to be put back in operation, after the resin has had time to cure 'm the formation and consolidate it.

While this invention is particularly useful in the consolidation of loosely consolidated formations surrounding the borehole of producing Wells, it may also be applied where the formation to be treated surrounds an injection well. lt may also be applied when a formation surrounding a borehole is to be treated for purposes other than consolidation, eg., for plugging a formation where the ow of fluids is to be prevented, or for treating a formation with an epoxy resin to improve its permeability to the flow of oil.

Referring to the drawing, the sole ligure of the drawing schematically illustrates a section through a borehole and a formation being treated. The point in time illustrated is that at which all of the polyepoxide solution has just been displaced into the formation and the gel plug has arrived at the exposed surface of the formation. In the drawing, a formation lil is penetrated by borehole ll, A casing l2, cemented in place by means of cement ld, is arranged in the borehole and is perforated by perforations l5 communicating with the formation to be treated. Dependent in the bore hole is tubing i6 which is perforated at the lower end thereof with perforations .lg and which carries straddle packers 19 and 2?, capable of isolating a section of the borehole within formation l@ opposite the perforations of the casing.

As illustrated in the drawing, several fluids have been pumped into formation lil in sequence. The fluid which had been first pumped in the formation is a water-displacing iluid 2l; the next fluid is a spacer fluid 22; the next fluid is the hydrocarbon solution of polyepoxide and curing agent previously described, shown as 24. As each solution is pumped into the formation through perforations 15, it fills the interstices between the grains of the formation around the borehole; each subsequent solution displaces the previous solution from these interstices. Ultimately there is thus formed a treated section having approximately the shape of a doughnut, in which the innermost layer contains the epoxy resin-curing agent solution.

As stated, it is highly desirable that the treating iluid which consolidates the unconsolidated formation be effective in the formation immediately adjacent to the borehole. It is equally apparent that it is impractical to leave treating solution in the borehole itself, since resin would gradually precipitate from the solution and ll the borehole with an extremely tough, hard and dillicult to remove resin plug. As' illustrated in the drawing, the problem is solved according to this invention by following the resin solution down the borehole with a gelled plug 2S, which in turn is followed by any displacing fluid 26, such as water, mud, or oil.

If no gel plug is present it is necessary to estimate the point at which the last portion of treating fluid has passed into the formation by calculation from knowledge of the dimensions of the borehole and depth of the penetrated portion thereof. This makes it rather diilicult to provide consistently precise placement of the solution. By adoptv ing the method of this invention, in which a gel plug follows the treating solution, a substantial pressure rise is immediately registered in the ultimate displacing fluid at the moment the gel plug reaches the penetrations, since the gel is substantially more difficult to pump into the formation than the polyepoxide solution. When the pressure increase is registered, indicating that all the treating solution has been just displaced into the unconsolidated formation, the pumps are shut down and the well is retained in shut-in conditon for the period of time required for resin to precipitate from the solution and consolidate the sand. This is usually about 24 to 36 hours. After the well has been shut in for the required period of time, production of the well is usually initiated either by permitting the pressure of the formation to displace the remaining fluid up through the borehole or by pumping the well.

In a preferred Inode of practicing this invention, the gel plug is made up such as to return to the liquid state in the desired period at the bottom of the borehole. Normally when a well is first produced, the gel or decomposed gel is first removed, the portion of the resin solution which was not precipitated as part of the resin, i.e., the major proportion of the solvent, is then removed from zone 2d through the borehole, followed by displacing fluid 22, water-removing iluid 2l and the formation fluids.

It has been found that complete consolidation of highly unconsolidated formations can be obtained when the method just described is carried out with a suitable solution of a polyepoxide and an amine curing agent. The precision of the treatment is such that substantially no sand is produced from the well immediately after the period of well shut-in is terminated. The strength of the consolidated formation increases for several days as a small amount of solvent which remains in the resin in the formation is gradually leached out therefrom by the formation uids. The formation then retains its high compression strength for an indenite period and can be produced at maximum rates permitted by the condition of the reservoir without resulting in sand being produced from the formation.

One of the advantages of the use of epoxy resins in the manner of Havenaar and Meys` over the use of phenolic resins for the consolidation of earth formations is that all reactants required to produce the resinous cement are present in a single batch of liquid. While it may be desirable to pretreat the formation to be consolidated with a water-displacing liquid and to follow this with a spacer liquid as has been illustrated, these do not exert any significant chemical action on the earth formation, serving merely to remove any unbound water from the formation. The reactants used to produce the desired resin coating on the sand grains are a polyepoxide and an amine which acts as a curing agent therefor. These reagents are preferably used in hydrocarbon solution. The composition of the solution is calculated to be such that no precipitation of resin occurs therefrom until the solution has been injected into the formation.

The amine which is employed as curing agent has the property of imparting surfactant characteristics to the partially cured resin which precipitates from solution. The amine is preferably employed in at least molar excess over the amount stoichiometrically required to react with all the epoxy groups of the uncured polyepoxide. By preparing the polyepoxide-amine solution in this manner, the bond between precipitated resin and the earth formation is greatly improved in all those cases in which the sand grains of the earth formation are in the condition normally found after excess water has been displaced.

If precipitated resin were present in the solution when it reaches the formation it would tend to cause undesired fracturing of the formation. It is, therefore, an important aspect of the process that the treating solution is prepared in a controlled manner to prevent any precipitation of solid resin prior to the time it is completely injected into the formation to be treated. This is accomplished by carefully selecting the type and concentration of solvent, polyepoxide, curing agent and promoter, and by preventing contact of the solution, prior to injection into the formation, with materials which would precipitate resin therefrom.

The total amount of polyepoxide and curing agent in such solutions is between 3 and 50 volume percent of the solution. The constituents of the solution are selected such that the viscosity of the solution is below centipoises at formation temperature.

The solvents in which the polyepoxide and curing agent are dissolved are most suitabiy hydrocarbon solvents containing a substantial proportion of aromatic hydrocarbons, preferably at least 50% by volume. VThe solvent is suitably a mix-ture of aromatic hydrocarbons or mixture of aromatic hydrocarbons and other saturated hydrocarbons. Suitable aromatic hydrocarbons are benzene or derivatives thereof, eg., alkyl benzenes such as toluene, xylenes and the like. Other suitable aromatic hyrocarbons are those obtained by extraction of aromatics from kerosene, gas oil, spindle oil, lubricating oil or heavy catalytically cracked cycle oil. A particularly useful solvent is a kerosene extract boiling in the range from 350 to 510 F., e.g., an SO2 extract of kerosene having an API ,gravity of 25-28, an initial boiling point between 350 and 390 F., an end point between 450 and 510 F., and an aromatic content of at least about 80% by weight, the remainder being saturated non-aromatic hydrocarbons. As explained in more detail hereinafter, the hydrocarbon solution may be prepared from such aromatic solvent with admixture of hydrocarbon containing a greater proportion of non-aromatics, eg., unextracted kerosenes, gas oils or the like. In general, oils boiling above and preferably between 350 and 650 F. are employed as solvents herein.

The polyepoxides used comprise those organic materials possessing more than one vic-epoxy group, i.e., more than one o 0/ C I groupi These materials may be saturated or unsaturated, aliphatic, cycloaliphatic, aromatic or heterocyclic.

Polyepoxides and particularly those of the polymeric type, can be described in terms of epoxy equivalent value, which refers to the number of epoxy groups contained in the average molecule. The meaning of this expression is described in U.S. 2,633,458.

lr the polyepoxide consists of a single compound and all of the epoxy groups are intact, the epoxy equivalency will be integers, such as 2, 3, 4 and the like. However, in the case of polymeric type polyepoxides many of the materials can contain some of the monomeric monoepoxides or have some of their epoxy groups hydrated or otherwise reacted and/or contain macromolecules of somewhat different molecular weight so that epoxy equivalent Values may be quite low and contain fractional values. The polymeric material, may, for example, have epoxy equivalent values such as 1.5, 1.8, 2.5 and the like.

Examples of the polyepoxides include, among others, 1,4-bis(2,3epoxypropoxy)benzene, 1,3-bis(2,3epoxypro poxy)benzene, 1,4bis(2,3-epoxypropoxy)diphenyl ether, 1,8 bis(2,3epoxypropoxy)octane, 1,4bis(2,3epoxypro poxy)cyclohexane, 4,4bi-s(2-methoxy-3,4-epoxybutoxy) diphenyl dimethylmethane, 1,3-bis(4,5epoxypentoxy)-5- chlorobenzene, 1,Lt-bis(3,4-epoxybutoxy)benzene, and 1,4- bis(2-methoxy-4,5-epoxypentoxy)benzene.

Other examples include the epoxy polyethers of polyhydric phenols obtained by reacting a polyhydric phenol with a halogen-containing epoxide or dihalohydrin in the presence of an alkaline medium. vPolyhydric phenols that can be used for this purpose include, among others, resorcinol, catechol, hydroquinone, methyl resorcinol, or polynuclear phenols, such as 2,2-bis(4hydroxy phenyl) propane ,(Bisphenol A) 2,2-bis(4hydroxypheny1) butane, 4,4-dihydroxybenzophenone, bis(4hydroxyphen yl)ethane, 2,2-bis(4hydroxyphenyl)pentane, and 1,5-dihydroxynaphthalene. rl`he halogen-containing epoxides may be further exemplified by 3-chloro-1,2epoxybutane, 2-bromo-1,2epoxyhexane, 3-chloro-1,2epoxyoctane, and the like.

The monomer products produced by this method from dihydric phenols and epichlorohydrin may be represented by the general formula o o CrCHCH2-OR-O-CH2-C \CH2 wherein R represents a divalent hydrocarbon radical of the dihydric phenol. The polymeric products will generally not be a single simple molecule but will be a complex mixture of glycidyl polyethers of the general formula oIrz-CH-oHg-o(R-o-CHToHoH-oHg-o)R-o-CHr-oH-Oru wherein R is a divalent hydrocarbon radical of the dihydric phenol and n is an integer `of the series 0, 1, 2, 3, etc. While for any single molecule of the polyether n is an integer, the fact that ythe obtained polyether is a mixture of compounds causes the determined Value for n to be an average which is not necessarily zero or a Whole number as noted above.

The aforo-described preferred glycidyl polyethers of the dihydric phenols may be prepared by reacting the required proportions of the dihydric phenol and the epichlorohydrin in an alkaline medium. The desired alkalinity is obtained by adding basic substances, such as sodium or potassium hydroxide, preferably in stoichiometric excess, to tlie epichlorohydrin. The reaction is preferably accomplished at temperatures within the range of from 50 C. to 150 C. The heating is continued for several hours to effect the reaction and the product is then Washed free of salt and base.

Preferred members of the above-described group of polyepoxides are the glycidyl polyethers of the dihydric phenols, and especially 2,2-bis(4hydroxyphenyl)propane, having an epoxy equivalency between 1.0 and 2.0, a molecular Weight between 250 and 900, and preferably a Durrans Mercury Method softening point no greater than C. Most preferred are the normally liquid products having a molecular Weight of about 350 to 400 and an epoxy equivalent of about 1.85.

The glycidyl polyethers of polyhydric phenols obtained by condensing the polyhydric phenols with epichlorohydrin as described above are also referred to as ethoxyline resins. See Chemical Week, Vol. 69, page 27, for September 8, 1951.

Another group of polyepoxides that may be used comprises the glycidyl ethers of novolak resins, which resins are obtained by condensing an aldehyde with a polyhydric phenol. A typical member of this class is the epoxy resin from a condensate of formaldehyde and 2,2- bis(4hydroxyphenyl}propane novolak resin.

The curing agents to be used to combine with the abovedescribed polyepoxides are amines which act both as a surface-active material to impart surfactant properties to the partially cured resin products, and as a curing agent to convert the polyepom'de to an insoluble infusible form. Preferred materials include those organic materials possessing a plurality of amino hydrogen groups, i.e., a plurality of groups, wherein N is an amino nitrogen. 'Ihese include lthe aliphatic, cyciloaliphatic, 4aromatic or heterocyclic polyamines as Well as derivatives thereof so long as the derivative still contains the necessary amino hydrogen.

Especially preferred for use in this invention are the polyamines possessing one or more cycloaliphatic ring, such as, for example, 1cyclohexylamino-aminopropane, 1,4-diaminocyclohexane, 1,3-diaminocyclopentane, bis-(3- methyl-4-aminocyclohexyl)methane, bis(4 aminocyclohexy1)methane, di(aminocyclohexyl)sulfone, 1,3-di(ami nocyclohexyl)propane, 4isopropyl1,2-diarninocyclohexane, 2,4-diaminocyclohexane, N,N'diethyl1,4diamino cyclohexane, and the like. Preferred members of this group comprise those polyamines having at least one amino or alkyl-substituted amino group attached directly to a cycloaliphatic ring containing from 5 to 7 carbon atoms. These cycloaliphat-ic amines are preferably obtained by hydrogenating the corresponding aromatic amine. Thus di(aminocyclohexyl)methane is obtained by hydrogenating methylene dianiline. Use of these amines is described in further detail in U.S. 2,817,644 to Shokal et al. The amines are especially preferred because they react rather slowly with the preferred epoxides in hydrocarbon solution, and thus provide ample time for the solution to be pumped into the earth formation to be treated, even in deep Wells and those most resistant to injection of fluid. As explained hereafter, in more detail, the time of first precipitation of resin from solution of such amines with polyepoxides can be shortened to a desired extent by addition of cure accelerators.

Other specially suitable amines which give better control over the rate of cure at relatively high temperatures are the aromatic polyamines, such as 1,3-diaminobenzene, 1,4-diaminobenzene, 4,4diaminodiphenyl, 1phen ylamino3aminopropane, di-4-aminophenyl methane, di- Zarninophenyl methane, di 3 methyl-4-aminophenyl methane and di-4-aminophenyl sulfone.

Various other amine curing agents which impart similar properties to the solution may be employed.

As the rate at which the epoxy compound reacts with the curing agent varies with temperature, and as the period required to inject a solution containing the epoxy compound and the curing agent from the top of a Well to the formation to be consolidated varies with the depth of the formation as Well as with the rate at which such solution can be injected into said formation, the period of time `during Wluch separation of the intermediate resinous product out of the solution Will not take place has to be controllable Within wide limits so that, on the one hand, in deep Wells no separation of resin will take place before the solution has entered into the formation (which would result in a plugging of the Wall of the formation), and on the other hand, when consolidating formations which are at a shallow depth, not too much time Iwill be lost before the consolidation begins to take place.

Preferably tests are carried out to find out the percentages of epoxy compound, curing agent, solvent and promoter for controlling the reaction rate which Will give the :best results under the conditions, eg., temperature, depth and porosity, set by the formation to be consolidated.

Vfhen consolidating part of an underground formation surrounding a well bore by the method according to the present invention, connate Water, i.e., water adhering to the grains of the formation due to capillary forces, may be present in such formation. It is preferred to remove the connate water before applying the resin solution to that part of the formation surrounding the well bore by flushing that part of the formation with a waterremoving fluid.

Preferably a spacer fluid is injected after the waterremoving uid but prior to the injection of the resin solution.

In order to prevent untimely precipitation of epoxy resin, the spacer iiuid has to be soluble in the resin solution and non-reactive with the ingredients thereof. Further the spacer fluid should be mutually soluble with the water-removing fluid as thereby the water-removing fluid containing the connate Water is effectively driven out by if* the spacer lluid from the part of the formation to be consolidated. In general it can be said that each injected liuid preferably is soluble in the following fluid so as to ensure that finally only the resin solution is present in the part of the formation to be consolidated or treated.

The water-removing lluid may be an oil solution of a surfactant. A preferred surfactant for this purpose has the formula R-l`\lll--(CH2)3--NH2, where-in R is an alkyl group derived from coconut oil, soya oil or tallow. A different group of suitable Water-removing iluids are organic liquids, such as hydrocarbon-oxygen compounds having less than 6 C-atoms per molecule and containing at least one lieto-oxygen group and/or hydroxyl group; suitable members are acetone, methyl ethyl ketone, isopropyl alcohol, n-propyl alcohol, sec-butyl alcohol, and the like.

The gelled fluid plug which is used to displace the epoxy-curing agent solution into the formation may be of any suitable chemical composition. By virtue of its physical state it cannot react to a significant extent With the epoxy solution in the borehole. Suitable gels can be aqueousor oil-based gels or may contain both Water and oil.

A suitable aqueous gel may be prepared, for example, by adding sodium borate and guar gum to sea water; this results in a gel plug which lasts for approximately -24 hours at the bottom of a typical well borehole.

A suitable oil-based gel may be prepared, for example, by adding an aluminum soap, such as a strearate, to a suitable oil, such as diesel oil.

Other suitable gels may be prepared by dissolving a mixture of fatty acids, such as tall oil acids, in a diesel oil, and converting them to their soaps therein. An especially good gel of this type is a mixture of diesel oil and 15% hydrochloric acid with a small amount of an emulsifying agent, preferably inorganic emulsifier such as 2% of a non-ionic polyamide. Suitable proportions are, for example, about diesel oil to about 70% acid, with 2% of polyamide as emulsilier.

Numerous other methods of gelling hydrocarbon or aqueous liquids are known to the art and may be success-fully employed in producing the gelled plug employed in the process of this invention, since as has been stated, the chemical composition of the gel plug is not a critical limitation.

Gels of the type described are well known to workers skilled in this art. They may be categorized as mixtures, one component of which is a fluid, homogeneous down to substantially colloidal dimensions, capable of resisting a vfinite shearing force. Technically, the liquid gels used in this process may also be viscous sols. While their chemical composition is not generally significant, it is desirable to avoid those which could adversely affect the part of the earth formation with which they come in contact, e.g., by plugging it with fine solids or by attacking it chemically.

en an aqueous gel plug is employed, it is preferable to follow the plug with an aqueous displacing liuid. For example, a plug based on sea Water, such as has been mentioned above, is suitably displaced down through the borehole by sea Water. A non-aqueous plug, such as one based on diesel oil, is suitably pumped down the Well by following it with a hydrocarbon fluid such as, for example, diesel oil or crude oil.

The following illustrates the application of the method of this invention to consolidation of sand surrounding an oil Well. The oil-producing formation is a clean, Well developed, sand s.ringer in the Miocene N series. The interval to be consolidated in the Well is a 9-foot Stringer, of which 6 feet is periorated.

Prior to preparing the epoxy solution, the initial resin separation time for solutions of 12% of a liquid polyepoxide reaction product of Bisphenol A and epichlorolrydrin and 6% bis(3 nethyl-l-aminocyclohexyl)methane in an aromatic solvent with varying amounts of diesel oils and phenol are determined bottom hole temperature of about 164 F. The aron.- ic solvent is an SO2 extract or" kerosene containing about 1% aromatics. The weil crude oil being not completely soluble in diesel oil, a 50-50 blend of diesel oil and kerosene extract is used as a first Wash in well treatment. rhis blend dissolves all the components of the crude.

The treatmei is designed to consolidate a cylinder 3 feet in radius and 9 feet in depth, the entire thickness of the sand stringer. The sand is first Washed with 3 pore volumes extract. This is followed by an equal volume of isopropyl alcohol to remove any remaining Water from the formation. A spuccr of l pore volume of the 50-50 blend is pumped into the formation to separate the ulcohol from the resin solution. The polyepoxide solution. is mixed to have an initial resin separation time sulicient to permit it to be pumped into the formation. About l.l pore volume of the treating solution is placed into the formation. The fluid pumped into the borehole immediatel following the treating solution is a plug of sea Ware. gelled by addition of sodium berate and guar gum. This plug is forced to the bottom and pumping discontinued as soon as a pressure rise indicates that the gel plug has reached the formation. The well pressure is balanced with sea water. The well is then shut in for 24 hours. The plug dissolves after about this period. When pressure is released on the Well, the fluids begin to unload immediately. Thus swabbing is not required to bring the well into production. On a l-hour production test, only 6.2% BS. shakeout is obtained. Altnough similar sand had been effectively retained by other in -"^ods, those Wells have produced large amounts of sand during cleanup until bridging occurs. This Well produces sand free immediately. ln this well as in other wells subsequently treated, substantially sand-free production has been obtained for several months and there is no indication that the consolidation treatment will not prevent the Well from sanding up during the remainder of its producing life.

ln another well treatment, a similar series of uids, including as the solution a solution of polyepoxide and curing agent in an aromatic hydrocarbon solvent, is displaced into the formation by following the treating solution with a gel plug of diesel cil gelled with an aluminum soap. The plug is forced to the bottom, and pumping discontinued after a pressure rise indicates that the plug has reached the formation. Pressure in the Well is balanced with diesel oil in the tubing. The well is then shut in for 24 hours.

As before, treatment chemicals are unloaded immediately when the Well is opened with very little sand being brought into the sand trap at the Well head. Such a well has been brought up to full production in stages over a period of a few days and has continued to produce gas condensate and Water with no further sand Droduction. Q

I claim as my invention:

l. In the method of treating a porous earth formation penetrated by a borehole, which comprises the steps of pumping into said formation a solution comprising a polyepoxide which is capable of being cured to a hard, cross-linked, hydrocarbon-insoluble cured resin, and a curing agent therefor, and maintaining said solution in said formation until epoxy resin has precipitated andV hardened in said formation, the improvement which comprises (l) pumping into said borehole, immediately following said resin solution, a gelled displacing fluid, (2) continuing to pump fluid into said borehole only until all of said resin solution has entered said formation and said gelled uid has just come in contact with the earth formation surrounding said borehole, as indicated at the surface by an increase in of the blend of diesel oil and kerosene.

the pressure required to pump further iiuid into said formation, and

(3) discontinuing further rise is observed.

2. A method according to claim l in which said solution of polyepoxide and curing agent is preceded in the treatment of the Well first by a iiuid which displaces substantially all unbound water from said formation and then by a spacer fluid in which both said first fluid and Said resin-curing agent solution are soluble.

3. A method according to claim 1 in which said polyepoxide is a normally liquid polyepoxide having more than one vicinal epoxy group per molecule, Which is the product of the reaction of 2,2-bis(4hydroxyphenyl)pro pane and epichlorohydrin in an alkaline medium, and said curing agent is a hydrogenated aromatic polyamine which is capable of acting as curing agent for said polyepoxide, the total amount of polyepoxide and curing agent being between 3 and 50 volume percent of said solution and said amine being present in said solution in an amount exceeding by at least 5 mol percent the stoichiometric equivalent of said polyepoxide.

4. The method according to claim l in which said gel is of a composition that breaks down to a free-flowing uid after being exposed for a predetermined time to the well conditions of temperature and pressure at the level of the formation being treated.

5. A method according to claim 1 in which said gelled uid is an aqueous gel.

6. A method according to claim 5 in which said gel is composed of sodium borate, guar gum and sea Water in gel-forming proportions.

pumping after said pressure 7. A method according to claim 1 in Which said gelled uid is an oil-based gel.

8. A method according to claim 7 in which said gel is composed of an aluminum soap and oil in gel-forming proportions.

9. Irl the method of treating a porous earth formation penetrated by a borehole, which comprises the steps of pumping into said formation a solution comprising a polyepoxide which is capable of being cured to a hard, crosslinlred, hydrocarbon-insoluble resin, and maintaining said solution in said formation in contact with a curing agent until epoxy resin has precipitated and hardened in said formation, the improvement which comprises (1) pumping into said borehole, immediately following said resin solution, a gelled displacing lluid,

(2) continuing to pump fluid into said borehole only until all of said resin solution has entered said formation and said gelled uid has just come into Contact with the earth formation surrounding said borehole, as indicated at the surface by an increase in the pressure required to pump further fluid into said formation, and

(3) discontinuing further pumping after said pressure rise is observed.

References Sited in the le of this patent UNITED STATES PATENTS 2,815,815 Hower Dec. 10, 1957 3,003,555 Freeman Oct. l0, 1961 3,047,067 Williams July 31, 1962 3,070,163 Colby Dec. 25, 1962 

1. IN THE METHOD OF TREATING A POROUS EARTH FORMATION PENETRATED BY A BOREHOLE, WHICH COMPRISES THE STEPS OF PUMPING INTO SAID FORMATION A SOLUTION COMPRISING A POLYEPOXIDE WHICH IS CAPABLE OF BEING CURED TO A HARD, CROSS-LINKED, HYDROCARBON-INSOLUBLE CURED RESIN, AND A CURING AGENT THEREFOR, AND MAINTAINING SAID SOLUTION IN SAID FORMATION UNTIL EPOXY RESIN HAS PRECIPITATED AND HARDENED IN SAID FORMATION, THE IMPROVEMENT WHICH COMPRISES (1) PUMPING INTO SAID BOREHOLE, IMMEDIATELY FOLLOWING SAID RESIN SOLUTION, A GELLED DISPLACING FLUID, (2) CONTINUING TO PUMP FLUID INTO SAID BOREHOLE ONLY UNTIL ALL OF SAID RESIN SOLUTION HAS ENTERED SAID FORMATION AND SAID GELLED FLUID HAS JUST COME IN CONTACT WITH THE EARTH FORMATION SURROUNDING SAID BOREHOLE, AS INDICATED AT THE SURFACE BY AN INCREASE IN THE PRESSURE REQUIRED TO PUMP FURTHER FLUID INTO SAID FORMATION, AND (3) DISCONTINUING FURTHER PUMPING AFTER SAID PRESSURE RISE IS OBSERVED. 